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7/29/2019 Soil Investigations.pdf
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Soil investigations for assessing the design
Prof G L Sivakumar Babu
Department of Civil Engineering
Indian Institute of Science
Email: [email protected];
Mobile No 9448480671
7/29/2019 Soil Investigations.pdf
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Ob ectives
to ground? How to use them in the analysis of civil
engineering structures
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Geophysical Methods
Mechanical Wave Measurements Crosshole Tests (CHT)
Downhole Tests (DHT) Spectral Analysis of Surface Waves
Seismic Refraction
Suspension Logging
Electromagnetic Wave Techniques Ground Penetrating Radar (GPR)
Electromagnetic Conductivity (EM)
Surface Resistivity (SR)
Magnetometer Surveys (MT)
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Mechanical Wave Geophysics Nondestructive measurements (s < 10-4%)
-
types (conducted across surface).
Measurements of wave dispersion:
velocity, frequency, amplitude, attenuation.
Determine layering, elastic properties,
, , Four basic wave types: Compression (P),
S ear S , ay e g , an ove .
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Mechanical Wave Geophysics Compression (P-) wave is fastest wave;
.
Shear (S-) wave is second fastest wave.
Is irectiona an po arize . Most
fundamental wave to geotechnique. Rayleigh (R-) or surface wave is very close
to S-wave velocit 90 to 94% . H brid
P-S wave at ground surface boundary.
-
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Mechanical Body Waves
P-wave
S-wave
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Mechanical Body Waves
S RTime
Oscilloscope
SourceReceiver (Geophone)
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Mechanical Waves (Compression)
P - Wave Velocities
Weathered Rocks
Intact Rocks
Steel
Till
Ice
Sea Water
Clay
Sand
0 1000 2000 3000 4000 5000 6000 7000 8000
Fresh Water
Compression Wave Velocity, Vp (m/s)
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Mechanical Waves (Shear)
S - Wave Velocit ie
Weathered Rocks
Intact Rocks
Steel
Till
Ice
Sea Water
Clay
Sand
0 1000 2000 3000 4000
Fresh Water s =
Shear Wave Velocity, VS (m/s)
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Geophysical Equipment
Seismograph Spectrum Analyzer
Portable Analyzer Velocity Recorder
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Seismic Refraction
oscilloscope
Note: Vp1 < Vp2
t1t2
Determine depthto rock la er z
Source
(Plate)
t3t4
il: V
x1x2 xx4zR
Rock: Vp2
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Seismic Refraction
0.020
)
xV Vc p2 p1
0.015
econd
1
2
V V
c
p2 p1
0.010
Time(s p2
m/s
0.005
Travel
1 Depth to Rock:
c = .
0.000
0 10 20 30 40 50
p1 =m/sc = .
alues
Distance From Source (meters)
x values
t
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Shear Wave Velocity, Vs
Fundamental measurement in all solids
, , , ,
Initial small-strain stiffness represented
by shear modulus: G0 = Vs2alias G = G = G
Applies to all static & dynamic problems at
- s Applicable to both undrained & drained
loading cases in geotechnical engineering.
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Seismic
Equipment
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Crosshole TestingOscilloscope
ASTM D 4428
Pump
t x = fctn(z)from incl inometers
Downhole
Vs = x/tHammer(Source) Velocity
TransducerTest
Receiver)xpackerSlo e
PVC-casedBorehole
PVC-casedBorehole
Note: Verticality of casing
must be established by
slope inclinometers to correctdistances x with depth.
InclinometerInclinometer
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Testing Equipment
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Downhole TestingOscilloscopePump
with normal load
tx
Hammer
packerz2
Test
Depth
Interval
HorizontalVelocity
Transducers
eop oneReceivers)
Shear Wave Velocit : R12 = z12 + x2
Cased
Borehole
Vs = R/t 2 = z2 x
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In-Situ Surface Wave Testing
Signal
Analyzer
SensorsSource
Accelerometer
L a y e r 1
RayleighSurface
L a y e r 2
aves a y e r L a y e r 4
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Shear Wave Measurements
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Seismic Piezocone Test (SCPTu)
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Seismic Piezocone Test
Obtains Four Inde endent
VsMeasurements with Depth:Hybrid of Penetrometer
one ress, qt Penetration Porewater Pressure,u Sleeve Friction, fs
60ou12 Arrival Time of Downhole Shear
Wave, ts
qc
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Automated Seismic Source
Electronically-actuated Self-contained Left and rightl i tiolarization Modified beam uses finto enhance shear wavegeneration Successfully tested todepths of 20mepths of 20m Capable of being usedwith traditional impulsehammerammer
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Sounding Memphis, Shelby County, TN
0 10 20 30 40
q t (MPa)
0 100 200 300
fs (kPa)0 1000 2000 3000
u2 (kPa)
0 100 200 300 400
Vs (m/sec)d = 35.7 mm
5 5 5
0
5Vs
10
15
h(m
)
10
15
10
15
10
15 fs
20
25
Dept
20
25
20
25
20
25
u2
30
35
30
35
30
35
30
35
qt
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Seismic Flat Dilatometer (SDMT)
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Geophysical Methods
Electromagnetic Wave
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Electromagnetic Wave Geophysics
Nondestructive methods
Non-invasive; conducted across surface. Measurements of electrical & ma netic
properties of the ground: resistivity
, , ,
and magnetic fields.
over w e spec rum n requenc esHz < f < 1022 Hz).
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Electromagnetic Wave Geophysics
Surface Mapping Techniques:
Ground Penetrating Radar (GPR)
Electrical Resistivity (ER) Surveys
Electromagnetic Conductivity (EM)
Downhole Techniques
Resistivity probes, MIPs, RCPTu 2-d and 3-d Tomography
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Ground Penetrating Radar (GPR)
GPR surveys conducted on gridded areas
Pair of transmitting and receiver antennae Short im ulses of hi h-fre EM wave
Relative changes in dielectric properties
.
Depth of exploration is soil dependent (up
to 30 m in dry sands; only 3 m in wetsaturated clay)
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Ground Penetrating Radar (GPR)
Xadar Sensors & Software GeoRadar
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Penetrating Radar (GPR)
Crossing an underground utility corridor
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Penetrating Radar (GPR)
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Ground Penetrating
Radar GPR
Geostratigraphy
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Examples of Ground Penetrating Radar (GPR)
Use u in Locating Un ergroun Uti ities
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Results from Ground Penetrating Radar (GPR)
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Results from Ground Penetrating Radar (GPR)
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Electrical Resisitivity Measurements
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Electrical Resistivity (ER) Surveys
Resisitivity R (ohm-m) is an electrical.
Arrays of electrodes used to measure
c anges in potentia .
Evaluate changes in soil types and variationsin pore fluids
, ,
sinkholes), stratigraphy, contaminant plumes.
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Resisitivity
easuremen s
What will be gained by
changing electrode
spac ng
Depth of ER survey:i.e., greater spacingn uences eepe
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Electrical Resisitivity Measurements
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Electrical Resisitivity Measurements
Resistivity Values (ConeTec & GeoProbe, 1997)
Glacial Till
Weathered Rocks
Loose Sands
Sands & Gravels
Loam
1 10 100 1000 10000
ay
Bulk Resistivity, (ohm-meters)
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lect ical Resistivit
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Electromagnetic Conductivity (EM)
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Magnetometer Surveys (MS)
Measure relative changesn e ear s magne c
field across a site.
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Applicability of In-Situ Tests
SPT
CLAYS SILTS SANDS GRAVELS Cobbles/Bould ers
ethod
CPT
u
Test DMT
In-Si
VST
0.0001 0.001 0.01 0.1 1 10 100 1000
Geophysics
ra n ze mm
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Equivalent Elastic Modulus
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Equivalent Modulus with Strain Level
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Equivalent Modulus for Monotonic Loading
1
o
0.8
o,G
/G
Cyclic
0.4
0.6
usRat
Monotonic
0.2Modul
Loading
0
1E-06 1E-05 0.0001 0.001 0.01 0.1
Shear Strain
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Conclusions
Knowledge of state of ground and stateof structure is enhanced usin extensive
instrumentation
instrumentation is are useful to design
,
structures under complex stress and